Perception of color is based in part on the color of available illumination sources. For example, when a person with typical color vision looks at a blue object illuminated by sunlight, the person is able to perceive the blue color of the object. This perception of the blue color is partially due to the object's reflection of the sunlight in the blue region of the visual spectrum. However, if the person views the same blue object illuminated by a red light source, such as an artificial red lamp, no light in the blue region of the visual spectrum is available to be reflected. Thus, the red light does not reveal the object's blue color, and the person perceives the blue object as dull and colorless. A color rendering index (CRI) is used to measure the ability of a light source to reveal the true colors of objects illuminated by that light source, where a higher CRI indicates a better ability to reveal true colors as compared to a lower CRI. For example, a CRI level of 100 (e.g., 100%) may indicate an excellent ability to reveal true colors of an object, while a CRI level of 1 (e.g., 1%) may indicate a poor ability to reveal true colors of an object. It may be advantageous for a light fixture to have a relatively high CRI, so that a person using the light fixture is able to perceive relatively accurate colors.
Lighting fixtures may produce different colors and/or color temperatures by combining light produced by multiple sources. For example, a light fixture that is designed for warm dimming may produce light across a range of light intensities and color temperatures (e.g., about 1800 K at lower intensities to about 5000 K at higher intensities) based on a user's control of the light fixture (e.g., a dimmer switch). The light fixture may provide color control by driving multiple groups of LEDs having different color temperatures. However, if the different groups of LEDs also have different CRIs, the light fixture may provide different color perception at different color temperatures. This may cause poor visibility of objects that are illuminated by the light fixture.
One technique for preventing different color perception at different color temperatures is to select all groups of LEDs to have similar CRIs. However, LED groups having a relatively high CRI may be more expensive than LED groups having a relatively low CRI, and selecting all LED groups with a relatively high CRI may result in a light fixture that is more expensive. In addition, selecting all LED groups with a relatively low CRI may result in a fixture that does not provide accurate color perception. Thus, it is desirable to develop techniques to provide a relatively low-cost light fixture with relatively high CRI across a range of color temperatures.